Tailgate: Description and Operation
Contact-free Tailgate Opening
Contact-free tailgate opening is a further tailgate operating element for the customer.
It is operated by moving a foot towards the bumper and then back again. Two sensors detect this movement in contact-free manner via a capacitive measurement.
The contact-free tailgate opening function has a forced connection to the SA322 Comfort Access.
A visual acknowledgement via the turn indicators is planned for a later point in time.
Brief component description
The following components for contact-free tailgate opening are described:
- Evaluation electronics on the local interconnect network bus
- Top and bottom sensor, contact-free tailgate opening
- Footwell module (FRM)
- Junction Box Electronics (JBE)
- Bumper aerial
Evaluation electronics on the local interconnect network bus
The evaluation electronics for contact-free tailgate opening are attached to the bumper support.
The sensors for contact-free tailgate opening are connected to the evaluation electronics. The evaluation electronics are connected to the footwell module (FRM) via the local interconnect network (LIN) bus. The evaluation electronics transmit the signal to open the tailgate to the footwell module.
The power distribution box in the junction box supplies the evaluation electronics with terminal 30.
Top and bottom sensor, contact-free tailgate opening
The two sensors are also attached to the bumper support. The top sensor is flat, the bottom sensor round.
The two sensors are connected to the evaluation electronics and continually measure the capacity. A comparison of the capacity measured over time allows the identification of certain movement patterns.
As a result, a targeted movement of the foot towards the bumper and back can be detected. The top sensor detects the shin, the bottom sensor the toes.
The detection range in the centre of the bumper is approx. 60 cm wide.
Footwell module (FRM)
The function for the contact-free tailgate opening is integrated in the footwell module control unit (FRM). The footwell module sends a bus signal to the junction box electronics to unlock the tailgate.
On Touring models without the SA316 automatic luggage compartment lid actuation, the rear window is unlocked.
Junction Box Electronics (JBE)
The central locking system for the tailgate is activated by a power output stage in the junction box electronics (JBE). The junction box electronics (JBE) unlock or lock the vehicle. The relays for unlocking and locking are located on the power distribution box. The junction box electronics (JBE) are plugged into the front power distribution box.
The local interconnect network bus from the evaluation electronics is routed through the junction box electronics (JBE).
For contact-free tailgate opening, the rear lid lock is supplied with current. The status of the central locking system does not change.
Bumper aerial
The Comfort Access function is integrated in the Car Access System control unit. With Comfort Access (SA322), the vehicle can be opened and started without actively using an ignition key. With Comfort Access, an ID transmitter is required instead of the usual remote control.
The bumper aerial is connected to the Car Access System (CAS).
If a contact-free tailgate opening operation is requested, the vehicle is woken up. A search for an ID transmitter is now initiated via the bumper aerials. If a valid ID transmitter is located in the rear area, the tailgate opens.
Functional networking
The following graphic shows the functional networking for contact-free tailgate opening.
System functions
The following system functions are described:
- Combination of the optional equipment
- Targeted foot movement
- Misuse protection
Targeted foot movement
For correct functioning, the foot must be inserted under the centre of the bumper and then withdrawn immediately.
The function is not carried out correctly under the following conditions:
- Foot movement outside the measuring range of the sensors (i.e. not in the centre of the bumper)
- Foot movement across the vehicle (weaving movement)
- Bumper is touched during the foot movement
- Foot left under the bumper for too long
- Foot not extended far enough under the bumper
Cycle protection
A cycle protection is implemented in the evaluation electronics as a protective function. A counter counts up to 5. The cycle protection covers incorrect operation and external disturbance variables. If the function is activated repeatedly by means of the foot movement but without a valid ID transmitter, contact-free tailgate opening is blocked for a certain time. The function only becomes available again when this time has expired or after a terminal change.
Definition of incorrect operation: Correctly executed foot movement, but without a valid ID transmitter in the area of the bumper aerial.
Notes for Service department
General notes
When retrofitting a trailer tow hitch, the footwell module (FRM) must be re-encoded. This adjusts the calibration.
Diagnosis instructions
The automatic luggage compartment lid actuation must be initialized after replacement of the control unit for the automatic luggage compartment lid actuation (HKL). Observe the service function in the diagnosis.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.